Design And Research Of Energy Harvester Applied To Low Frequency Vibration And Swing

The rapid development of wireless sensor networks(WSN)and the Internet of Things(Io Ts)has made more and more low-power electronic products appear in people’s daily life.However,how to provide continuous power supply is still the biggest obstacle restricting its use.There is a large amount of mechanical energy in the low-frequency vibration and swing of the surrounding environments.Harvesting mechanical energy and powering low-power electronic devices provides a potential solution.In recent years,environmental energy harvesting technology has received extensive attention from researchers.Various energy harvesters based on piezoelectric effect and electromagnetic induction have been proposed,but most of them have high operating frequencies,narrow operating bandwidths and poor energy harvesting effect under low-frequency conditions.In order to solve the above problems,this thesis first proposes a monostable hybrid energy harvester(HEH)composed of piezoelectric energy harvester(PEH)and electromagnetic energy harvester(EMEH),which aims at reducing the working frequency of the energy harvester,expanding bandwidth,improving its energy harvesting effect and adaptability under low-frequency excitations and capturing energy simultaneously from one excitation through the two power units.The energy harvester is mainly composed of a piezoelectric cantilever beam,two central magnets,two external magnets,two stoppers and two sets of coils.The theoretical model of the HEH is established in this thesis,and the simulation results are in good agreement with the experimental results.Under a harmonic excitation with amplitude of 0.5 g,the power output of the HEH is experimentally measured is higher than that produced by the individual power units when they work separately.Compared with the linear energy harvester,the operating frequency of the HEH shifts to low frequency,and the peak power is slightly increased,which makes the HEH very suitable for low-frequency energy harvesting.The mechanical energy in the environment not only exists in the form of vibration,but also in the form of swing.The second eccentric mass-driven rotor(EMDR)proposed in this thesis can convert ultra-low frequency vibration or swing motion into uni-directional high-speed rotation of the rotor.The ingenuity of the motion conversion mechanism lies in the design of the two-layer plectrum.When the entire eccentric mass rotates counterclockwise,the plectrum provides sufficient driving force which can make the rotor rotate at a high speed in uni-direction.And when the entire eccentric mass rotates clockwise,the friction force generated by the plectrum on the rotor structure is very small.EMDR-based rotational energy harvester(E-REH)is designed and fabricated.Compared with the conventional swing-based energy harvester(SBEH)without motion conversion mechanism,the electric output of the energy harvester under ultra-low frequency vibration and swing excitations is significantly improved.In addition,the designed energy harvester has a comparatively long duration of electric outputs after the continuous excitation is removed,making it adapt well to the practical excitation with intermittent availability.When the energy harvester is fixed to the arm or leg of the human body and the tester is jogging at speeds of 6 km/h and 9 km/h,the generated electric output can maintain the continuous operation of some electronic devices.The two energy harvesters proposed in this thesis can effectively convert the low-frequency vibration or swing in the environment into electric energy.The research has proved the application prospect of the energy harvester in realizing high-performance low-frequency energy harvesting.